`mapr diffstreams`

This utility compares the message IDs, metadata, and data in two HPE Ezmeral Data Fabric streams. Then, generates two directories that contain sequence files that you can use to merge the rows from the two HPE Ezmeral Data Fabric streams.

Sequence files are binary flat files. You can learn more about them here. To convert a sequence file into a format that you can read, use the HPE Ezmeral Data Fabric Database JSON FormatResult utility.

This utility considers both the source stream and the destination stream to be a master stream. Therefore, it generates two directories with sequence files. These sequence files contain the puts required to update each stream so that it contains a superset of the rows defined in both tables at the time at which the utility was run.

This utility generates both of the following output directories in the output directory that you specify:

opsForDst: A directory containing sequence files that correspond to each put and delete required to make the destination stream identical to the source stream.
opsForSrc: A directory containing sequence files that correspond to each put and delete required to make the source stream identical to the destination stream.

Required Permissions

To use this utility, you must have the following permissions:

The permission readAce on the volumes where the tables are located.
On the source stream: either consumeperm or copyperm.
On the destination stream: either consumeperm or copyperm.

For information about how to set permissions on volumes, see Setting Whole Volume ACEs.

For information about how to set permissions on streams, see Enabling Table and Stream Authorizations with ACEs.

NOTE The mapr user is not treated as a superuser. HPE Ezmeral Data Fabric Streams does not allow the mapr user to run this utility unless that user is given the relevant permission or permissions with access-control expressions.

Syntax

mapr diffstreams 
-src <srcStream>
-dst <dstStream>
-outdir <output directory>                           
[-first_exit] Exit when first difference is found
[-mapreduce true/false default:false]
[-numthreads <nthreads> default:16]

Parameters

Parameter	Description
src	The path of the first stream to include in the comparison.
dst	The path of the second stream to include in the comparison.
outdir	The path to a directory in which to place the generated sequence files. The utility creates the specified directory. If the specified directory already exists, the command fails.
first_exit	By default, the utility compares all the data in the specified streams. Use this parameter if you want to exit after the first difference is identified between the streams. The parameter takes no value.
mapreduce	A Boolean value that specifies whether or not to use a MapReduce program to perform the comparison. The default, preferred method is to use a MapReduce program (true). When this parameter is set to false, a client process uses multiple threads. The MapReduce program runs as a MapReduce version 2 application based on the MapReduce mode that is configured on this node.
numthreads	When -mapreduce is false, this parameter specifies the number of threads allocated to perform the comparison. The default is 16. If additional CPU resources are available, you might want to increase the number of thread to achieve better performance.